1. Field of the Invention
The present invention relates to audio processing techniques. More particularly, the present invention relates to systems and methods for extracting ambience from audio signals.
2. Description of the Related Art
Various techniques are available for extracting ambience components from a two-channel stereo signal. The stereo signal may be decomposed into a primary component and an ambience component. One common application of these methods is listening enhancement systems where ambient signal components are modified and/or spatially redistributed over multichannel loudspeakers, while primary signal components are unmodified or processed differently. In these systems, the ambience components are typically directed to surround speakers. This ambience redistribution helps to increase the sense of immersion in the listening experience without compromising the stereo sound stage.
Some prior frequency-domain ambience extraction methods derive multiplicative masks describing the amount of ambience in the input signals as a function of time and frequency. These solutions use ad hoc functions for determining these ambience extraction masks from the correlation quantities of the input signals, resulting in suboptimal extraction performance. One particular source of error occurs when the dominant (non-ambient) sources are panned to either channel; prior methods admit significant leakage of the dominant sources in such cases. Another source of error in prior methods arises from the short-term estimation of the magnitude of the cross-correlation coefficient. Short-term estimation is necessary for the operation of mask-based approaches, but prior approaches for short-term estimation lead to underestimation of the amount of ambience.
What is desired is an improved method for ambience extraction.